Method of piercing type for hobbing punches



- March-18, 1958 l. A. SMITH METf-IOD OF 'PIERCING .TYPE FOR HOBBING PUNCHES Filed Jan. 20, 1954 .I' .Z. jjg/z g y 7 ax/w a Z \W/% u m 5 1% INVENTOR" MW "IjTORNEYO United States. Patent 7 METHOD OF PIERCING TYPE FOR HOBBING PUNCHES Ian A. Smith, Williamantic, Conn., assignor to American Screw Company, Providence, R. I., a corporation of Rhode Island ApplicationJanuary 20, 1954, Serial No. 405,077

2 Claims. (Cl. 76-107) The present invention relates to die-sinking and particularly to the formation of dies or types for the cold hobbing of punches used in the cold heading of recesse screws and the like, the ultimate product being, for example, a recessed screw of the so-called Phillips type as described in United States Patent No. 2,474,994 granted to J. J. Tomalis. I

The types presently employed in the production of the header punches for making such screws are, in turn, formed by a method comprising the piercing of a block of suitable material by a master punch which has been carefully machined from a material of superior quality and hardness. This method often requires that piercing be performed in several stages before proper penetration is achieved. After each stage, the punch must be removed, cleaned, lubricated and replaced in the type with exact orientation, all of which requires time and careful attention, adding to the cost of producing the types in question.

If greater force is employed, for the purpose of avoiding the multi-step procedure just outlined, it is found that the die material falls away from the advancing punch or, in other Words, fails to conform accurately with the true slope and contour of the punch, resulting in the formation of a die or type which is inaccurate and therefore is incapable of forming header punches which are precise reproductions of the master. punch. The inaccuracy of the resulting screw-head recesses is somewhat greater, the inaccuracies of the type being increased in magnitude by virtue of the double transfer thereof, which inaccuracy of the screw-head recesses constitutes a commercial disadvantage which may asume serious proportions.

Attempts have been made to overcome the described difficulty by compensating the master punch for the expected failure of the die material to conform thereto, but this method of correcting the error is, of course, empirical and inherently untrustworthy. The main object, therefore, of the present invention is the provision of a method of piercing dies which eliminates the cause of the difficulty by ensuring that the material of the die, in receding before the impact of the master punch, nevertheless maintains close engagement with the latter and is thereby provided with a recess which is a true reciprocal of the punch form.

The die must of course be machined after piercing, to remove any metal which hasbeen extruded above the mouth of the recess or die cavity and to provide the desired flat or curved surface in the area surrounding the recess.

More specifically, it is an object of the invention to provide a method of piercing dies comprising the steps of pressing a punch into a block of die-forming material, thereby displacing outwardly and upwardly a portion of said material, applying pressure to said displaced die material over an annular area immediately surrounding 2,826,940 Patented Mar. 18, 1958 the punch and simultaneously applying equal pressure to said punch to cause the displaced material to fill all depressions of the punch as the latter effects further penetration of said block, removing said pressure, and withdrawing said punch.

Other and further objects, features and advantages will be apparent from the description which follows, read in connection with the accompanying drawings in which Figures 1, 2 and 3 are diagrammatic sectional views illustrating successive phases of the invention;

Figure 4 is an enlarge fragmentary view corresponding to Figure 3; and

Figures 5 and 6, respectively, illustrate finished dies for making header punches for fiat head and round head screws.

In order to facilitate an understanding of the invention, reference is made to the embodiments thereof shown in the accompanying drawings and detailed descriptive language is employed. It will nevertheless be understood that no limitation of the invention is thereby intended and that various changes and alterations are contemplated such as would ordinarily occur to one skilled in the art to which the invention relates.

In Figures 1-4, inclusive, the block of die or type material, for example of steel having the necessary characteristics, is designated at 10. The master punch 11 is slidably but tightly surrounded by a bushing 12 which in turn is similarly held in a punch holder 13. A filler plug 14 fits in the bushing 12 on top of the punch 11,

In the first step of the method, after the several elements are assembled as shown, a downward force is applied to the plug 14, forcing the plug and the punch 11 downwardly relative to the bushing 12 and holder 13. The punch penetrates the die block 10, causing the partial formation of a depression therein and a corresponding upward and outward fiow of metal to form the swelling 15 around the perimeter of the recess which raises the bushing 12 somewhat as seen in Figure 2. The application of pressure to the plug and punch, only, in this phase of the operation, permits a relatively unrestricted initial How of the die material which is desirable to avoid distortion or failure of the punch and to eliminate shearing and improper grain disposition in the die itself. As a result of this step, the plug 14 is substantially flush with the top of bushing 12.

In the next step of the method, pressure is applied simultaneously to the plug 14 and the bushing 12, causing a slight further penetration of the punch and, at the same time, squeezing the metal of the swelling 15 into the space between the bushing 12 and the wings 17 of the punch, causing this metal to conform closely to all surfaces of that part of the punch nib which penetrates below the surface 18 of the block 10. This operation results in the formation of a die cavity or recess 19 which is the exact counterpart of the punch nib.

The punch, punch holder and associated parts are then removed and the die is machined to produce a finished surface, in the area of the cavity 19, corresponding to the desired header punches to be formed in the die. These may be designed to punch recesses in fiat head screws, in which case the die is finished as seen in Figure 5, or round head screws (see Figure 6), or still another type of screw head, the die surface 18 being finished accordingly.

The method of the invention is carried out as a continuous operation on any suitable hydraulic press or similar apparatus, and it is not necessary to remove and reinsert the punch, as described above, or to apply pressure in several intermittent stages as heretofore done.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. Method of cold piercing dies comprising the steps of pressing a punch into a block of die-forming material, thereby displacing outwardly andtupwardly a portion of said material, applying pressure in the punching direction to said displaced die material over an annular area immediately surrounding the punch and simultaneously applying equal pressure directly to said punch causing the punch to effect further penetration of said block and causing the displaced material to fill all depressions of the punch as the latter eflects further penetration of said block, removing said pressure, and withdrawing said punch.

2. Method of cold piercing dies comprising the steps of pressing a punch into a block of die-forming material, thereby displacing outwardly and upwardly a portion of said material, applying pressure in the punching direc- 4 v tion to said displaced die material over an annular area immediately surrounding the punch and simultaneously applying equal pressure directly to said punch causing the punch to effect further penetration of said block and causing the displaced material to fill all depressions of the punch as the latter effects further penetration of said block, removing said pressure, withdrawing said punch, and machining the surface of said block in the area surrounding the recess formed by said punch.

References Cited in the file of this patent UNITED STATES PATENTS 1,771,610 Blakeslee July 29, 1930 2,014,698 Reilly Sept. 17, 1935 2,066,372 Tomalis t Jan. 5, 1937 2,140,670 Donbeck Dec. 20,1938 2,325,989 Tryon Aug. 3, 1943 2,638,019 Stellin May 12, 1953 

